1. Field of the Invention
This invention relates to ultrasonic imaging apparatus which nondestructively observes an internal state, such as a defect or the like, within an object to be inspected using a focused untrasonic beam.
2. Description of the Prior Art
The configuration of such an ultrasonic imaging apparatus is shown, for example, in U.S. Pat. No. 4,953,405.
In a conventional procedure of nondestructive ultrasonic inspection, particularly by ultrasonic imaging, the focus point of a focused ultrasonic beam is first adjusted to a depth to be observed within an object to be inspected. Subsequently, in a plane display (C-mode) image, only an echo signal from a depth range to be observed is depicted while removing echo signals from the upper and lower surfaces of the object, and a time gate is set in order to configure an ultrasonic image.
According to the above-described operations, an ultrasonic echo signal and a time gate signal are displayed on the display surface of an oscilloscope. The operator gradually changes the distance between an ultrasonic transducer and the object, and adjusts the start point and time width of the time gate while observing the signals. Electronic-scanning-type ultrasonic medical diagnostic apparatuses are also known, wherein the focus point of an ultrasonic beam is displayed on a cross-section display (B-mode) image using a marker.
The above-described conventional appproaches, however, have the following problems.
(1) In, order to know the depth range within an object to be inspected to which an observed plane display image corresponds, or to provide an image of a predetermined depth range of the object, it is necessary to process an ultrasonic signal displayed on an oscilloscope, read the position of the signal on the time base, and calculate the actual depth. PA1 (2) Iris also necessary to calculate to which depth within an object to be inspected the focus of an ultrasonic beam is adjusted by observing the waveform of an ultrasonic signal on an oscilloscope display in the same manner as in item (1). PA1 (3) If the position of a defect within an object to be inspected cannot be predicted in advance, it is necessary to repeat the operations shown in items (1) and (2) in the range between the upper surface and the lower surface of the object.
Since the above-described operations require knowledge of ultrasonic techniques and are complicated, an expected image cannot be obtained if the operations are not adequately performed. Hence, such operations are disadvantageous in applying the ultrasonic imaging method.